All the stock ballcups have been staying on my car. SOme got sloppy real fast (front) so I put teflon tape between the ball and cup. I also used teflon tape on the axles and pins to keep the plastic hexes on-works Great.
Now-in the back-you might be popping the ball-cup off if your long on hub-and you havent shaved off the inside of hub for clearance. YOU also might need to make the ballcups a tad shorter to run short on hub and middle or outer holes on tower.
I have been slowly eplacing all my ballcups with the ones that come in the sway bar kit. Very tight fit on the ball and no clearnace issues!!